Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/66—Silver or gold
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/48—Silver or gold
  • B01J23/50—Silver
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D301/00—Preparation of oxiranes
  • C07D301/02—Synthesis of the oxirane ring
  • C07D301/03—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds
  • C07D301/04—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds with air or molecular oxygen
  • C07D301/08—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds with air or molecular oxygen in the gaseous phase
  • C07D301/10—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds with air or molecular oxygen in the gaseous phase with catalysts containing silver or gold

Definitions

• the present invention relates to the production of olefinic oxides and to the preparation of a carrier-based silver catalyst for the catalytic oxidation of olefines to form olefinic oxides, particularly for the oxidation of ethylene to form ethylene oxide.
• the direct combination of ethylene with oxygen can be effected with mixtures containing a wide range in the ratio between air and ethylene by using suitable catalysts, such as, for example, finely divided silver or silver oxide.
• Ethylene oxide is obtained from a partial oxidation of ethylene. Unfortunately, however, part of the oxidation goes to completion, resulting in large amounts of carbon dioxide and water, aside from other secondary reaction products such as aldehydes, etc. From the mixture of these reaction products, ethylene oxide can be separated invarious ways.
• Catalysts of this type have the disadvantage that a purely mechanical mixing of silver with dispersing agents or adeposition of thermic decomposition of silver compounds upon porous material do not guarantee that the fine subdivision will be maintained for a long time under the high temperature conditions to which the catalytic surfaceiis exposed during the synthesis of ethylene oxide.
• variations of the catalytic activity cannot be avoided. Such variations are caused by sintering or other altering processes which take place upontextended nse'or under the influence of excessiveheath Itis an; ob'ect, or" the resent invention to ure are a new silver catalyst which, when used inthe catalytic oxidation of ethylene,is free.
• the catalyst of this invention is prepared in a simple and practical manner by co-precipitating a silver salt from the aqueous solution of a silver salt, together with an excess of another inert substance which, upon precipitation, forms particularly fine crystals.
• a silver salt from the aqueous solution of a silver salt, together with an excess of another inert substance which, upon precipitation, forms particularly fine crystals.
• Such a substance should neither tend to sinter or to dissociate at high temperatures, and should be practically stable up to 600 C.
• alkalineearth carbonates are primarily met by the alkalineearth carbonates, although the invention is not restricted to these compositions. If, for example, silver carbonate and calcium carbonate are precipitated together under suitable conditions, a co-precipitate is obtained which, after drying, constitutes a conglomerate of extremely fine particles having an average diameter equal to, or smaller than, 5 microns.
• the silver and alkaline-earth salts to be used for precipitating the carbonates must be free from or substantially free from impurities actingupon. silver as catalytic poisons such as, for instance, chlorine and sulfur. Small quantities of chlorine within conventional purity limits are allowable, however.
• the catalytic powders produced in this manner consisting of silver carbonate and alkaline-earth carbonates, may be used as they are, for example pressed into tablet form, or they may be embedded within natural or arti ficial porous aggregates such as quartz, alundum and, particularly, carborundum refractory materials.
• an improved catalyst is prepared when the catalytic powder is caused ot adhere to, and penetrate into, the interstices of the porous carrier by means of a special procedure which is a still further object of the present invention.
• the co-precipitated powder consisting of silver carbonate with at least 60% of calcium carbonate, is suspended in a mixture of water and a polyvalent alcohol such as ethylene glycol, and is caused to adhere to the porous carrier material by means of a suitable treatment, for instance by stirring grains of the carrier material into the suspension and removing excess liquid by filtering under vacuum.
• a suitable treatment for instance by stirring grains of the carrier material into the suspension and removing excess liquid by filtering under vacuum.
• the moist catalyst grains obtained in this manner, are placed in a drying oven and are heated, from /2. to 3 hours, to a temperature between 200 and 500 C.
• This thermic treatment for the catalytic activation of the silver co-precipitate diilers from the known thermic processes of decomposing silver compounds primarily because the dissociation of the silver carbonate is checked in the presence of the evaporating liquid while, atthe same time, an activating reduction to silver oxide is effected by reaction with the polyvalent alcohol, which results in a particularly efiicacious product.
• Catalysts prepared in the foregoing manner have the further advantages of possessing superior oxidation activity, particularly with respect tothe olefines, together with a high selectivity, probably due to thev greatly increased total surface area. of the spherical silver particles.
• the catalysts show immediately highest efiiciency without the need of further conditioning. Although they can be used without detriment at a relatively high temperature, they give particularly good conversions and produce high synthesis yields at low temperatures, such as slightly -above200 C. i
• the catalysts of this invention particularly suitable for employment in synthetic processes conducted under pressure;
• the greatest difliculty in pressure synthesis consists, generally, in maintaining strict control of the reaction temperature because of the heat liberated in the process, the greater part of which results. from the complete, combustion of the olefines.
• Prior investigators have proposed 7 the addition of steam or other gases as reaction moderapurposes. While continuously stirring, the mixed suspension is evaporated to dryness on a water bath.
• Example 2' I p 7 20 gr. of silver nitrate are dissolved in 200 fccm. of Water and a silver carbonate precipitate is formed, while j stirring, by adding'62' ccm. .of'a 10% aqueous sodium carbonate solution. The precipitate is thoroughly washed with water, filtered and oven-driedjat 108 C. The resulting silver carbonate powder is placed into a vitreous glass. funnel and mixed into a suspension with"50% aqueous glycol and a 100 ccm. measure of a siliceous refractory material of a grain size suitable for catalytic purposes.
• The. conversion of ethylene to ethyleneoxide amounts to 15.3%,with a 37.4% yield.
• the term spatial velocity? indicates'th'e number of volumes: of gas, measured. at
• This operation is performed in such a man-
• the operation is carried out in such a manner that,while the'ret'ractory material is intimately mixed with the catalyst, the excess liquid is eliminated by applying a slight suction to the vitreous glass funnel.
• the refractory material thus covered with powder is placed into a muffle oven and heated to 400% C. for one hour.
• a mixture of 3% ethylene with air is passed over 100 ccm. of the catalyst prepared in this manner, at a spatial velocity of 330 liters/hour and about 7 seconds contact time, whereby the catalyst is maintained at a reaction temperature of 210 C.
• Example 5 parts of silver nitrate and 80 parts of calcium nitrate are dissolved together in 1000 parts of water.
• 42 parts of a 10% solution of sodium carbonate are dropwise added while stirring.
• the precipitate is separated by means of a vitreous glass tunnel under vacuum and is washed several times, while vigorously stirring, until the wash Water has a pH of 6.5. After drying the precipitate in an oven at 108 C., 45 parts of powdery material are obtained.
• Example 6 From an aqueous solution containing silver nitrate and calcium nitrate at a molar ratio of 4:1, silver and calcium carbonate is precipitated according to the procedure of Example 5. After washing and filtering, the precipitate is dried in an oven at 108 C. 45 gr. of the dry catalytic powder are placed in a vitreous glass funnel and are mixed into a suspension with a aqueous ethylene-glycol solution and 100 ccm. of granulated green carborundum having a particle size of about 3 mm. in diameter. The operation is carried out in such a manner that the excess liquid is eliminated by applying a light vacuum to the filtering funnel while the carborundum is intimately mixed with the catalyst.
• the carborundum is thus'homogeneously covered with the catalyst powder.
• the grains are then introduced into a muflie oven and heated for an hour to 400 C.
• water or water-glycol vapors developed, containing oxidation products of the glycol from the reaction with the silver compounds; care must be taken that this atmosphere be maintained over the catalyst until the end of the heating.
• Example 7 A catalyst prepared according to the method of Example 6 is charged into a reaction tube 300 cm. long and 12 mm. in diameter. Upon passing through this tube an ethylene-air mixture containing 3-4% ethylene, at a spatial velocity equal to 410 liters/hour under atmospheric pressure and at a reaction temperature of 230 C., of the ethylene employed is converted to gees-pier ethylene oxide in a single passage at a yield in excess of Example 8 By operating according to Example 7 but increasing the spatial velocity to 820 liters/hour, the conversion to ethylene oxide falls to 50% while the yield is about the same as in Example 7, i. e. in excess of 70%.
• Example 9 An eth Example 10 The catalyzer efficiency does not change during a continuous test covering a period of over 3000 hours and under operating conditions as set forth in Example 6.
• the silver nitrate and calcium nitrate should be present in the mixture at a molar ratio between 1:1 to 1:4, preferably exceeding a ratio of 111.5.
• Cur preferred carrier for the catalytic silver compound consists of carborundum aggregates of uniform particle size, which are more than 2 mm. and, preferably, 3 mm. in diameter.
• the quantity of silver carbonate-calcium carbonate coprecipitate deposited on and within the carrier may range from 15 to gr. but is, preferably, about 45 gr. for ccm. measure of a granulated carrier having Broadly speaking, the quantity of deposited corecipitate will change with the particle size of the carrier. if the weight ratio between calcium carbonate and silver in the catalytic mixture is about 2.7:1, approximately one-fourth of the mixture consists of silver. Consequently, the catalyst carrier contains 5 to 15 gr. but, preferably, about 10 gr. of silver for every r00 ccm. measure thereof.
• the particle size of the mixed catalyst powder made according to this disclosure is 5 microns and less. Consequentiy, the adherence of the powder to the surface of the carrier and within the interstices of the carrier is excellent. Thus, if a quantity of the finished catalytic material is dropped from a height of 3 meters, the amount of catalytic powder separated from the granular carrier is practically negligible.
• the catalytic activity of the heroin claimed product is such that a 100 ccm. measure of the catalyst containing about 10 gr. or" silver, is capable of oxidizing within one hour about 300 gr. of ethylene to ethylene oxide.
• the temperature of this catalytic oxidation may range from to 300 C., but is preferably held between 200 and whe in 1 o g n et l ne atin ranging .from 10:1 to 1:1.
• the comminution of the silver precipitate, as well as the homogeneous and dispersion of the particles, is attained by co-dispersing at least an equimolar amount, but preferably an excess, of calcium carbonate with silver carbonate in a fluid dispersion medium and removing the fluid dispersion medium to obtain a solid dispersion of silver carbonate in a calcium carbonate powder of equally small particle size.
• the resulting catalyst is superior to prior, similar catalysts not only in producing ethylene oxide at an increased conversion ratio and higher yield because of its selective action, but in displaying increased physical stabilityygreater resistance to high temperatures and pres- .sures and exceptionally high stability in operation, coupled with a substantial reduction in the quantity of silver required ,for a given production output.
• .-We claimz H 1 'A'process for preparing a carrier-based silver catalyst suitable for the catalytic oxidation of olefines comprising the steps of preparing an aqueous solutioncontaining' a silver salt and an alkali earth salt at a molar ratio from 1:1 to 1:4, dropwise adding,-while stirring, a sodium carbonate solution to co-precipitate silver carbonate and alkali earth carbonate, washing the co-precipi- .tate until the wash water has a pH of 6.5, drying the coprecipitate, forming asuspension of the co-precipitate in an aqueous solution of a member of the group consisting of glycerol and ethylene glycols mixing'a granular, porous refractory material into the suspension, causing the coprecipitate to adhere to the refractory material by vacuum tering said aqueous solution, and heating the coated refractory material to between 200 and 500 C.
• a process for preparing a carrier based silver catalyst suitable for the catalytic oxidation of olefines comprising the steps of preparing an aqueous solution containing about 2% of silver nitrate and about 8% of calcium nitrate, dropwise adding, while stirring, a 10% aqueous solution of sodium carbonate to co-precipitate silver carbonate and calcium carbonate, washing'the co-precipitate until the wash water has a pH of 6.5, drying the coprecipitate at about 108 C., forming a suspension of the co-precipitate in a 50% aqueous solution of ethylene glycol, mixing granular carborundum aggregates of a particlesize of about 3 into thesuspension, causing the co-precipitate to adhere to the carborundum aggregates by vacuum filtering said aqueous ethylene glycol solution, and'heatingthe coated oarborundum aggregates for 5 about 1 hour to 400 C.
• a carrier-based silver catalyst for the catalytic oxidation of 'olefines to olefine oxides consisting of granulated, poroussiliceous refractory material as the carrier anda coating which penetrates into the interstices of said material and consists of a; homogeneous mixture of decomposition products of silver carbonate and at least 50% of an alkali earth carbonate, each 100 cc. of saidmaterial containing an amount .of said decomposition products of silver carbonate comprising 5-15 gr. of silver.
• a carrier-based silver catalyst for'th'e catalytic'oxidation ofolefines to olefine Ioxides consisting of granular, carborundum aggregates of a particle size from 2 to 3' mm. as the carrier and a coating of a homogeneous mixture of '-30% of decomposition products of silver carbonate and 80-70% of calcium carbonate, said mix ture having a'particle size of not more than 5 microns, each 100 ccm. of aggregates containing an amount of said decomposition products ofsilver carbonate comprising about 10 gr. of silver.
• a carrier-based silver catalyst for the catalytic oxidation of olefines'to olefine oxides consisting ofgranular carborundum aggregates of a particle size of about 3 nim. as the carrier and a'coating which penetrates into the interstices of saidaggregates andconsists of a homogeneous mixture of.2030% of decomposition products of silver carbonate and -70% of calcium carbonate,
• a carrier-based silver catalyst for the catalytic oxidation of olefines to olefine oxides consisting of granular, porous refractory material of a particle size of about 3, mm. as the ,carrienQcoated with a homogeneous mixture of 1 part'of decomposition products of silver carbonate and about 2.7 parts; of calcium carbonate, each 100 ccm. of, said granular refractorymaterial containing 15 to 75 gr. of said coating.
• y V V 7 A carrier-based silver catalyst for.

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Cited By (17)

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• 1954
  • 1954-07-23 DE DEM23894A patent/DE1064046B/de active Pending
  • 1954-07-23 FR FR1110846D patent/FR1110846A/fr not_active Expired
  • 1954-08-03 US US447664A patent/US2825701A/en not_active Expired - Lifetime
• 1956
  • 1956-09-12 FR FR57656A patent/FR75801E/fr not_active Expired

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